Equilibrating Immigration and Anthracene-Maleimide-Based Diels

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Equilibrating Immigration and Anthracene-Maleimide Based Diels-AlderTrapping of Octylmaleimide in Mixed Photo-Crosslinked Polymer Micelles Jinqiang Jiang, Yan Liu, Min Tian, Huan Chang, Xiang-Yang Yan, Zhao-Tie Liu, and Zhong-Wen Liu Langmuir, Just Accepted Manuscript • Publication Date (Web): 25 Nov 2014 Downloaded from http://pubs.acs.org on November 25, 2014

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Equilibrating Immigration and Anthracene-Maleimide Based Diels-Alder-Trapping of Octylmaleimide in Mixed Photo-Crosslinked Polymer Micelles Yan Liu, Min Tian, Huan Chang, Jinqiang Jiang,* Xiangyang Yan, Zhaotie Liu, Zhongwen Liu

Key Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education. School of Chemistry & Chemical Engineering, Shaanxi Normal University, Xi’an, Shaanxi, China, 710062. Tel.: 86-29-81530784; fax: 86-29-81530784. E-mail address: [email protected]

ABSTRACT: It is possible that the hydrophobic guest within amphiphilic polymer micelles may leak out and be captured by other species before polymer micelles adhere to the desired focus because of the complexity in an actual release procedure, rendering the reduced efficiency of nano-carrier system. To describe such a scenario, two water-soluble fluorescent amphiphilic random copolymers of PAV and PAA with photo-crosslinkable coumarin and anthracene pendants, respectively, were chosen to investigate the equilibrating immigration and maleimide-anthracene based Diels-Alder-trapping of hydrophobic octylmaleimide guest from one type of photo-crosslinked polymer micelles of PAV85% to another of PAA66% in aqueous solution using the emission and absorption spectra techniques.

KEYWORDS: Polymer Micelles; Photo-Crosslinking; Equilibrating Immigration; Diels-Alder Reaction; Hydrophobic Trapping

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1. Introduction Over the last few decades, amphiphilic polymer micelles have emerged as viable platforms for the encapsulation and delivery of hydrophobic molecules in nano-carrier system.1-7 For this purpose, polymer micelles must efficiently encapsulate hydrophobic guests until they adhere to the desired focus.4,

8-9

It’s known that the inherent loading capacity of polymer micelles in

aqueous solution can be fine-tuned by slight variations in amphiphilic polymer structure parameters, such as hydrophobic content in amphiphilic polymer. However, the hydrophobic guest in micellar aqueous solution itself is just an indicator of the thermodynamic distribution between polymer micelles and the bulk solvent.10-14 This means that hydrophobic guests in nano-carriers may leak out after being administrated in the body due to the extreme dilution or other factors, rendering any strategy for site-specific transport of polymer micelles useless.15-18 Therefore, understanding the thermodynamic distribution of hydrophobic encapsulation can provide some crucial implications to nano-carriers. Thayumanavan and co-workers have established an elegant method to evaluate the stability of drug delivery vehicles. They succeeded in evaluating the dynamic exchange of hydrophobic fluorescent molecules within nano-assemblies in aqueous solutions using a fluorescence resonance energy transfer (FRET) based method.18-20 However, it is also possible that the hydrophobic guest may be captured by other species before polymer micelles adhere to the desired focus because of the complexity in an actual release procedure, also resulting in the reduced efficiency of nano-carrier system. Herein, as our continuing efforts to develop photo-crosslinkable amphiphilic polymers, we sought to describe such a scenario by incorporation of the maleimide based fluorescence quenching effect within photo-crosslinked fluorescent


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polymer micelles to trace the hydrophobic guest immigration and the maleimide-anthracene based Diels-Alder addition to perform the thermal-induced guest trapping in mixed micellar system.

Figure 1. a) The schematic structures of two photo-crosslinkable fluorescent amphiphilic copolymers of PAV and PAA and the hydrophobic guest of n-octylmaleimide (OM). b) The equilibrating immigration of OM molecules from OM/PAV85% to PAA66% in the mixed micellar systems. c) The thermal-induced Diels-Alder-trapping of hydrophobic OM guest in mixed micellar systems.

As schematically shown in Figure 1, two photo-crosslinkable fluorescent amphiphilic random copolymers

of

PAV

and

PAA,

i.e.

poly[(2-acrylamido-2-methyl-propane


sulfonic

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acid-co-(7-(4-vinyl-benzyloxyl)-4-methylcoumarin)] and poly[(2-acrylamido-2-methyl-propane sulfonic acid)-co-(anthracene methyl methacrylate)], were independently self-assembled into nano-aggregates in aqueous solution and irradiated to form photo-crosslinked polymer micelles of PAV85% and PAA66%, respectively. And the fluorescence quencher of n-octylmaleimide (OM) was chosen as hydrophobic guest to be uploaded into PAV85% polymer micelles. Then OM/PAV85% was chosen as a maleimide source to mixed with PAA66% to form the mixed micellar systems, resulting in the equilibrating immigration of OM molecules from photo-crosslinked polymer micelles of PAV85% into PAA66%. Furthermore, when the mixed system was heated at 80 oC, the OM molecules would be trapped by PAA66% polymer micelles because of the thermal-induced anthracene-maleimide Diels-Alder addition. 2. Experimental section 2.1. Materials 2, 2-Azoisobutyronitrile (AIBN) was purified by recrystallization from 95% ethanol. n-Octylmaleimide (OM), 2-acrylamido-2-methyl-propane sulfonic acid (AMPS), 4-vinylbenzyl chloride, methacryloyl chloride, 9-Anthracenemethanol and 4-methylumbelliferone were purchased from Aladdin and used without further purification. Ultrapure water was prepared utilizing a FDY-1002-UV-P purification system. The anthracene methyl methacrylate (AM) and 7-(4-vinyl-benzyloxyl)-4-methylcoumarin (VBC) were prepared according to our previous works.21, 22 2.2. Characterization 1

H NMR (400 MHz) spectra were investigated by a Bruker spectrometer with d6-DMSO as

solvent.


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GPC was performed using a Waters system with DMF as eluent (0.5 mL min-1) and polystyrene as standard. Absorption spectra were measured with an Evolution 220 spectrophotometer (Thermo Fish Instrument Co., Ltd.). Fluorescence emission spectra were measured with a PTI fluorescence master system. The slit width was maintained at 0.75 nm for excitation and 0.50 nm for emission, respectively. The fluorescence spectra were taken with λex at 353 nm. Dynamic light scattering (DLS) measurements were performed with a Malvern Nano-ZS90 instrument (Malvern, U.K.) to determine the average diameter and size distribution of micelles at room temperature. AFM images of micelles were observed by a CSPM5500A scanning probe microscope system (Being Nano-Instruments Co., Ltd.) in the tapping mode. Samples were prepared by dropping the micellar solution onto mica sheets, and dried at room temperature overnight. The photo-crosslinking reaction of anthracene and coumarin pendants, respectively, was achieved by the irradiation of 365 nm LED light (Shanghai Huave Info-Tech Co., Ltd.) with mild stirring, the distance between the solution and the spot light was about 1.0 cm.

2.3. Synthesis of photo-crosslinkable fluorescent amphiphilic random copolymer of PAA To a 50 mL ampoule, AIBN (0.028 g, 0.17 mmol), AMPS (8.300 g, 40 mmol), AM (0.582 g, 2.1 mmol) and DMF/H2O (30 mL, V/V = 3/1) were quickly added. Then, the mixture was degassed, and filled with nitrogen. After 30 min stirring at room temperature, the ampoule was placed in a preheated oil bath (95 oC) for 30 h. The amphiphilic polymer of PAA was collected by precipitation twice into diethyl ether. The crude product was dialyzed against ultrapure water


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while stirring for three days; water was frequently refreshed (every 2 h during day time). Finally, the amphiphilic polymer was dried to constant weight under vacuum freeze drying condition. Yield: 70%. Mn = 2.44×104 g mol-1. Mw/Mn = 1.20 (GPC). 1H NMR (DMSO), δ (ppm): 8.35 (s, -NH-), 7.70-7.06 (m, aromatic H), 6.19 (s, -C(=O)-CH), 5.13 (s, -CH2O-). PAA was further estimated to compose of 114 AMPS and 3 AM units according to the calibration curve of AM in DMF (see S1 in the Supporting Information). 2.4. Synthesis of photo-crosslinkable fluorescent amphiphilic random polymer of PAV To a 50 mL ampoule, AIBN (0.023 g, 0.14 mmol), AMPS (6.218 g, 30 mmol), VBC (0.792 g, 2.7 mmol) and DMF/H2O (30 mL, V/V = 3/1 ) were quickly added. The synthetic process and post-treatment were same with the synthesis of PAA. Yield: 70%. Mn = 2.42×104 g mol-1. Mw/Mn = 1.20 (GPC). 1H NMR (DMSO), δ (ppm): 8.32 (s, -NH-), 8.00-7.17 (m, aromatic H), 6.86 (s, -CH2O-). PAV was further estimated to compose of 110 AMPS and 5 VBC units according to the calibration curve of VBC in DMF (see S2 in the Supporting Information).

2.5. Preparation of photo-crosslinked polymer micelles in aqueous solution Calculated amount of amphiphilic copolymers of PAV and PAA were independently and directly dissolved in aqueous solution to a concentration of 5.00 mg mL-1, and then conveniently photo-crosslinked using 365 nm LED irradiation to form photo-crosslinked polymer micelles of PAV85% and PAA66%, respectively. The percentage numbers here corresponded to the crosslinking densities, which were evaluated according to the characteristic absorption intensity changes of coumarin at 320 nm and anthracene at 390 nm (see Figure 2a), respectively. The size distributions of these polymer micelles (0.25 mg mL-1) were analyzed by DLS instrument at room temperature, and the micellar morphologies were observed with AFM images.


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2.6. Equilibrating immigration of OM molecules in the mixed micellar systems Calculated amount of PAA (50.00 mg) and n-octylmaleimide (15.00 mg) were added into water (10 mL) with mild stirring for 48 hours, and then the polymer aqueous solution was transferred carefully into another ampoule after standing for 2 hours. And 0.1 mL of polymer aqueous solution was mixed with 1.90 mL of 9-Anthracenemethanol DMF solution (0.31 mg mL-1) in the fluorescence cuvette and heated to 80 oC for 2 hours to trigger the anthracene-maleimide Diels-Alder addition while stirring, resulting in the estimation of the encapsulated OM molecules in PAA aqueous solution according to the decreasing absorption band intensity at 390 nm before and after heating. Then, calculated amount of PAA and water was added into the OM loaded polymer micelles with mild stirring for another 48 hours to prepare the specified weight percent OM loaded polymer micelles of PAA (4.00 mg mL-1). And the other three polymer micelles of OM/PAA66%, OM/PAV and OM/PAV85% with different weight percent OM encapsulation were prepared following the same procedure, and polymer concentrations were kept at 4.00 mg mL-1. These OM loaded polymer micelles were checked with absorption and emission spectra instruments while polymer concentration was diluted to 0.25 mg mL-1 with water. OM equilibrating immigration experiments were achieved by monitoring the fluorescence spectra changes (λex = 353 nm) of two sets of mixed micellar systems every 10 min for about two hours. For set one (S1), 0.75 mL of 0.5, 1.0 and 2.0 weight percent OM loaded micelles of PAV85% (0.50 mg mL-1) was mixed with 0.75 mL PAA66% (0.50 mg mL-1) in the fluorescence cuvette to form three mixed micellar systems of S1-1, S1-2 and S1-3, respectively; for set two (S2), 2.0 weight percent OM loaded micelles of PAV85% (1.00, 2.00, 4.00 mg mL-1) was mixed with PAA66% (0.50 mg mL-1) in the same volume and denoted as S2-1, S2-2 and S2-3, respectively.


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2.7. Diels-Alder-trapping of OM molecules in mixed micellar systems upon heating The above six mixed micellar systems were further heated from 25 oC to 80 oC within 1 min, then kept at 80 oC for two hours with mild stirring, resulting in the Diels-Alder addition between OM molecules and anthracene pendants within PAA66%. And the heating procedures were monitored with absorption spectra and emission spectra with λex at 353 nm. 3. Results and discussion 3.1. Preparation of Photo-Crosslinked Polymer Micelles in aqueous solution Coumarin and anthracene are well-known for their characteristic photo-dimerization reactions, which have been widely investigated for the application of photo-responsive materials.4,

23-35

Furthermore, polymer micelles can be stabilized by the photo-dimerization of coumarin or anthracene moieties incorporated in amphiphilic polymers.4 As designed, two photo-crosslinkable fluorescent moieties of coumarin and anthracene were introduced into the water-soluble amphiphilic polymers of PAV and PAA, respectively. And the polymers were independently dissolved in aqueous solution to form nano-aggregates and then photo-crosslinked to a certain degree with 365 nm light irradiations. Figure 2 showed the absorption and emission spectra of PAV and PAA before and after photo-crosslinking. As shown in Figure 2, polymer micelles in aqueous solution of PAV afforded a broad absorption band centered at 320 nm (log ɛ = 4.19), which decreased significantly after the photo-dimerization of coumarin pendants. On the other hand, PAA showed a highest absorption band around 256 nm (log ɛ = 4.94) with a shoulder at 285 nm and a series of vibrationally spaced absorption structures at 335, 353, 370 and 390 nm (finger like absorption bands), whose intensities (except for 285 nm) decreased after the photo-crosslinking reaction of anthracene pendants. And as shown in Figure


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2b, PAV polymer aqueous solutions showed a characteristic broad emission peak around 385 nm, which was greatly suppressed after photo-crosslinking; PAA showed a multiple emission band peaking at 399, 419 and 440 nm, whose intensities decreased by a third after the photo-crosslinking. These results indicated the different inherent electron properties of coumarin and anthracene chromophores in aqueous polymer micelles of PAV and PAA, respectively.

Figure 2. a) Absorption spectra of PAV (0.25 mg mL-1) and PAA (0.25 mg mL-1) in aqueous solution before and after photo-crosslinking. b) Fluorescence spectra (λex = 353 nm) of PAV (0.25 mg mL-1) and PAA (0.25 mg mL-1) in aqueous solution before and after photo-crosslinking.

The size distributions of polymer nano-aggregates in aqueous solution before and after photo-crosslinking were monitored by DLS instrument. As shown in Figure 3a, the average size of PAV (~ 920 nm) and PAA (~460 nm) decreased significantly to ~ 600 nm and ~400 nm after the photo-crosslinking of coumarin and anthracene pendants, respectively, revealing the photo-crosslinking effect in polymer micelles. And these polymer micelles were also visualized with nano-spheres by AFM images (see Figure 3b). The average diameter measured by AFM was much smaller than those measured by DLS at 25 oC. This discrepancy in size could be attributed to the fact that DLS data directly reflected the dimension of polymer nano-aggregates in aqueous


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solution, where hydrophilic chains were well dispersed in water with hydrophobic components loosely associating within water-soluble amphiphilic polymer micelles.

Figure 3. a) Size distributions of polymer micelles of PAV (0.25 mg mL-1) and PAA (0.25 mg mL-1) in aqueous solution before and after photo-crosslinking. b) AFM images for polymer micelles of PAV and PAA before and after photo-crosslinking.

3.2. Equilibrating immigration of OM molecules in mixed micellar systems Maleimide is known as one of the most efficient electron acceptors to electron-rich moieties, such as coumarin and anthracene, resulting in the fluorescent emission reduction of the donor chromophores.36-38 And as discussed above, since the coumarin and anthracene pendants in polymer micelles had different inherent electron properties, the resulted fluorescence quenching effect of OM to polymer micelles of PAA and PAV before and after photo-crosslinking should have various fluorescence quenching behaviors.


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Figure 4. a) Fluorescence spectra (λex = 353 nm) of OM loaded polymer micelles of PAA66% (0.25 mg mL-1). b) Plots of normalized I vs OM weight percentage in polymer micelles of PAV (0.25 mg mL-1) and PAA (0.25 mg mL-1) before and after photo-crosslinking.

And as shown in Figure 4a, when the hydrophobic electron acceptor of OM were encapsulated into polymer micelles of PAA66%, the multiple fluorescence emission band covering 380-540 nm intervals decreased gradually as a function of OM weight percentage without any significant peak shift, resulting in the evaluation of quenching effect of OM/PAA by the normalized emission intensities at 419 nm. Thus, the bigger the normalized I, the less quenching effect of OM to fluorescent polymer micelles. And as shown in Figure 4b, at the used conditions, the normalized I of OM/PAA and OM/PAV polymer aqueous solutions decreased linearly with a linear fit slope of -0.0331 and -0.0067, respectively, indicating the greater fluorescence quenching effect of OM/PAA than OM/PAV.

Interestingly,

the

fluorescence

quenching effect of two

photo-crosslinked polymer micelles of OM/PAA66% and OM/PAV85% were obviously greater than the corresponding precursor polymer micelles of OM/PAA and OM/PAV at lower OM weight percentage, then significantly suppressed with the increasing weight percentage of OM encapsulation, respectively. This could be attributed to two factors: one was that the photo-crosslinked polymer micelles contained fewer chromophores of anthracene and coumarin


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than the corresponding precursor of PAA and PAV, respectively; another was the “incarceration” effect generated by the photo-crosslinking, which could stabilize the polymer micellar structure and encapsulate more OM guest molecules within photo-crosslinked polymer micelles. Furthermore, OM/PAA66% showed a much greater exponential decay as a function of OM weight percent than OM/PAV85%, resulting in the ever increasing gaps of normalized I between OM loaded polymer micelles of PAA66% and PAV85%, respectively.

Figure 5. a) Fluorescence spectra (λex = 353 nm) of mixed micellar system of S1-3. b) Plots of normalized I of two set of mixed micellar systems as a function of mixing time.

The key motivation of OM immigration in mixed micellar system significantly depended on the thermodynamic equilibration of OM between two photo-crosslinked polymer micelles of PAA66% and PAV85%. Thus, if OM/PAV85% were chosen as the maleimide source to be mixed with non-loaded PAA66%, the OM molecules would immigrate from PAV85% into PAA66% because of the great concentration difference of OM in two polymer micelles, and the immigration speed would be slowed down along with the deceasing concentration difference. And, along with the increasing weight percentage of OM within PAV85%, more OM molecules would leak into PAA66% polymer micelles, resulting in the more decreasement of fluorescence intensity of the


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mixed system. As designed, the same volume of OM/PAV85% and PAA66% (0.50 mg mL-1) were mixed together and monitored with fluorescence emission spectra over the mixing time. And the mixed micellar systems were classified with set one (S1) according to the weight percentage (0.5%, 1.0% and 2.0%) of OM encapsulated in PAV85% (0.50 mg mL-1) and set two (S2) with the increasing polymer concentration (1.00, 2.00 and 4.00 mg mL-1) of 2.0 weight percent OM loaded micelles of PAV85%, and denoted as S1-1, S1-2, S1-3, S2-1, S2-2 and S2-3, respectively. As shown in Figure 5a, the multiple fluorescence emission bands of S1-3 covering 380-600 nm intervals decreased slightly but significantly as a function of mixing time, evidently confirming the immigration of OM molecules from PAV85% into PAA66% and resulting in the evaluation of OM molecule immigration by the normalized emission intensity at 419 nm. Figure 5b showed the time-dependent I values of mixed micellar systems in two hours. The OM molecule immigration was indicated by a gradual exponential decay of the normalized I. And it was clearly shown that the immigration of OM from PAV85% into PAA66% was proportionally accelerated as the increasing amount of OM encapsulated in PAV85% polymer micelles, and leveled off after 60, 80 and 100 min for S1-1, S1-2 and S1-3, respectively. The normalized I changes of S2 afforded almost the same decrease with S1-3 in the downhill stage in the initial 20 min mixing time, and then slightly accelerated as a function of the micellar ratio of OM/PAV85% to PAA66%. 3.3. Maleimide-anthracene based Diels-Alder-trapping of OM molecules in mixed micellar systems upon heating Other than the photo-dimerization upon light irradiation, another more intriguing aspect of anthracene is the ability to undergo both thermal and photochemical Diels-Alder additions with a variety of dienophiles, 39 especially maleimide, 40-41 across the 9 and 10 positions, resulting in the


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break of its conjugated structure. Which appears to be governed much more by temperature; however, higher temperatures above 90 oC can favor the retro Diels-Alder reaction. Thus, when upon heating at 80 oC, OM molecules will not only immigrate from PAV85% into PAA66%, but also be trapped by anthracene pendants through the anthracene-maleimide based Diels-Alder addition, which we called “Diels-Alder-trapping” of OM guest in mixed micellar systems. As shown in Figure 6a, the absorption spectra of two set of mixed micellar systems and PAA66% showed very similar weak shoulders at 370 and 390 nm belonging to the characteristic absorption bands of anthracene; furthermore, the characteristic band shape and intensity at 390 nm of six mixed micellar systems almost remained unchanged as against that of PAA66% despite of the different micellar ratio between OM/PAV85% and PAA66%. Which helped to trace the maleimide-anthracene Diels-Alder addition by monitoring the absorption spectra changes. And it was understandable that that the Diels-Alder addition would increase along with the increasing OM molecules in the mixed system. As shown in Figure 6b, the absorption band at 390 nm of S1-3 decreased obviously during the heating procedure, indicating the ongoing maleimide-anthracene Diels-Alder addition within polymer micelles of PAA66%. Furthermore, as shown in Figure 6c, the absorption spectra of OM/PAV85% almost showed no changes during the heating procedure. Therefore, the normalized intensity changes at 390 nm (I390) of anthracene can be chosen to evaluate the OM molecule trapping effect in mixed micellar systems. As shown in Figure 6d, the time-dependent I390 values of S1-1, S1-2 and S1-3 decreased vertically to 0.967, 0.954 and 0.938 during the initial 1 min heating procedure from 25 oC to 80 oC, and then decreased gently with a slope of -0.0001, -0.0002 and -0.0003 during the other 2 hour heating period at 80 oC, respectively, ascribing to a possibility of anthracene-maleimide Diels-Alder addition in the initial


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heating stage. S2 afforded three similar decrease of normalized I390 values during the initial 1 min heating stage, then presented faster exponential decay with the increasing micellar ratio of OM/PAV85% during the other 2 hour heating time.

Figure 6. a) Absorption spectra of OM/PAV85% (0.005, 0.25 mg mL-1), PAA66% (0.25 mg mL-1) and two set of mixed micellar systems. b) Absorption spectra changes of S1-3 during the heating procedure. c) Absorption spectra changes of OM/PAV85% (0.005, 0.25 mg mL-1) during the heating procedure. d) Plots of normalized I390 of the mixed micellar systems as a function of heating time.

Furthermore, the resulting succinimide groups of maleimide-anthracene addition would no longer exhibit a strong quenching effect. Thus, the OM trapping procedure could also be monitored by fluorescent emission instrument. As shown in Figure 7a, the multiple emission band of S1-3 was not always weakening during the heating procedure, which plummeted down at the


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beginning and then increased gradually upon further heating at 80 oC. As shown in Figure 7b, the time-dependent I values of S1 decreased vertically to 0.900, 0.850 and 0.765 during the initial 1 min heating procedure, respectively. Then S1-1 showed almost unchanged I values during the other 2 hour heating period at 80 oC, indicating that all of OM molecules may be trapped within the initial 1 min heating procedure. S1-3 afforded an quicker increasing I values than S1-2 as a result of more OM molecules being encapsulated in the mixed micellar system. And S2 also afforded similar I changes with the lowest at 0.740, 0.716 and 0.696 in the initial stage and the final at 0.834, 0.806 and 0.736 along with the increasing micellar weight ratio of OM/PAV85%. These “vertical down-gradual up” changes of normalized I were well consistent with the absorption spectra analysis in Figure 6d. And from the view point of molar ratio of OM to anthracene in mixed micellar systems (S1-2 corresponding to equimolar OM and anthracene), these results indicated that many of OM molecules in mixed micellar systems of S2 were not trapped by PAA66% polymer micelles during the 2 hour heating procedure at 80 oC.

Figure 7. a) Fluorescence spectra changes (λex = 353 nm) of S1-3 during heating procedure. b) Plots of normalized I at 419 nm of mixed micellar systems as a function of heating time.


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4. Conclusions In summary, two types of photo-crosslinked fluorescent polymer micelles were chosen to describe the hydrophobic guest immigration and molecular trapping in mixed micellar systems. Methods of absorbance and fluorescence spectra, DLS and AFM were applied. The results showed that OM molecules could present different fluorescence quenching effects to polymer micelles of PAV85% and PAA66%, respectively, resulting in the evaluation of OM molecular immigration from PAV85% into PAA66% by tracing the evolution of fluorescence quenching over the mixing time. And the OM trapping analysis by absorption and emission spectra showed a possibility of anthracene-maleimide Diels-Alder addition in the initial 1 min heating stage, however many of OM molecules were still not trapped by PAA66% polymer micelles during 2 hours heating procedure. Since the guest employed model the hydrophobic nature of drug molecules, this feature can provide some implications to the potential nano-carrier leakage and also renders photo-crosslinked polymers to be of great interest for controlled release applications in the area of pharmaceutical and biomedical research.

ACKNOWLEDGMENT. This work is supported by the Nature Science Foundation of China (NSFC 21374056), the Natural Science Basic Research Plan in Shaanxi Province of China (NSBRP-SPC 2014JM2051), the Fundamental Research Funds for the Central Universities (GK201302045), Shaanxi Innovative Research Team for Key Science and Technology (2012KCT-21, 2013KCT-17) and the One Hundred Plan of Shaanxi Province.

Supporting Information Available: Absorbance and FL spectra, DLS, AFM investment of polymer micelles. This material is available free of charge via the Internet at http://pubs.acs.org.


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Two photo-crosslinkable fluorescent amphiphilic copolymers of PAV and PAA were chosen to investigate the equilibrating immigration and maleimide-anthracene based Diels-Alder-trapping of hydrophobic octylmaleimide molecules in mixed photo-crosslinked polymer micelles.


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Equilibrating Immigration and Anthracene-Maleimide-Based Diels

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